Mutations of anaplastic lymphoma kinase (ALK) are thought to be involved in the development of subsets of numerous cancers including i) non-small cell lung carcinoma; ii) diffuse large B-cell lymphoma; iii) esophageal squamous cell carcinoma; iv) anaplastic large-cell lymphoma; v) neuroblastoma (a childhood cancer that arises from the developing peripheral nervous system); and vi) the sarcomas known as inflammatory myofibroblastic tumors (IMTs). Patient outcomes with many of these malignancies are poor, due in part to the late detection of the cancers because of the lack of efficient clinical diagnostic methods. Early detection and diagnosis of ALK-mediated cancers dramatically increases survival rates within the patient population; as an example, early detection of ALK-positive anaplastic large-cell lymphoma can result in survival rates of up to 83% whereas late detection is associated in some instances with survival of only 50% of the patient population. A technology that would allow for earlier detection of these cancers could greatly facilitate the medical management of the patients suffering from them, helping ultimately to improve their treatment outcomes. Both preclinical and early clinical data indicate that only those cancers that express activating ALK mutations that drive their development and progression exhibit robust antitumor responses to ALK small-molecule inhibitors.